Continuous, carbohydrate to ethylene glycol processes

ABSTRACT

By this invention processes are provided for the conversion of carbohydrate to ethylene glycol by retro-aldol catalysis and sequential hydrogenation using control methods having at least one of acetol (hydroxyacetone) and a tracer as inputs.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit under 35 U.S.C. § 119(e) to U.S.Provisional Application 62/905,068, filed Sep. 24, 2019, and entitledMETHODS FOR OPERATING CONTINUOUS, UNMODULATED, MULTIPLE CATALYTIC STEPPROCESSES, which is hereby incorporated herein by reference in itsentirety for all purposes.

TECHNICAL FIELD

This invention pertains processes for the catalytic conversion ofcarbohydrate to ethylene glycol by the retro-aldol/hydrogenation route.

BACKGROUND

Ethylene glycol is a valuable commodity chemical that has a broad rangeof uses as both a building block for other materials such aspolyethylene terephthalate (PET) and for its intrinsic properties suchas for antifreeze. Ethylene glycol demand is substantial, making it oneof the largest volume organic chemicals produced in the world. It iscurrently made by multistep processes which start with ethylene derivedfrom hydrocarbon feedstocks.

Proposals have been made to manufacture ethylene glycol from renewableresources such as carbohydrates. These alternative processes includecatalytic routes such as hydrogenolysis of sugar and a two-catalystprocess using a retro-aldol catalyst to generate intermediates fromsugar that can be hydrogenated over a hydrogenation catalyst to produceethylene glycol and propylene glycol.

In the retro-aldol route, carbohydrate is converted over a retro-aldolcatalyst to intermediates, and then the intermediates are thencatalytically converted over a hydrogenation catalyst to ethylene glycoland/or propylene glycol in an unmodulated reaction zone. As used herein,the term unmodulated means that the process is conducted in a single potor if in multiple vessels or regions, intermediates are not removedbetween vessels or zones. The sought initially-occurring retro-aldolreaction is endothermic and requires a high temperature, e.g., oftenover 230° C., to provide a sufficient reaction rate to preferentiallyfavor the conversion of carbohydrate to intermediates. Under conditionsthat favor the retro-aldol conversion, isomerization of sugars canoccur. For instance, aldose such as glucose, can be isomerized tofructose. Aldose, such as glucose, provide under retro-aldol conditionsintermediates containing 2 carbon atoms such as glycol aldehyde that canbe hydrogenated to ethylene glycol. Fructose, under retro-aldolconditions, is converted to, among other things, intermediatescontaining 3 carbon atoms that under hydrogenation conditions providepropylene glycol and glycerol. Additionally, retro-aldol intermediatessuch as glycol aldehyde can react to provide co-products such as1,2-butanediol. Moreover, hydrogenation can result in degradation ofethylene glycol and propylene glycol. And since hydrogen is required,mass transfer of hydrogen to catalytic sites may be inadequate tosupport the hydrogenation, and this hydrogen starvation can result inco-products such as organic acids being produced. Accordingly, tooptimize the production of ethylene glycol in an unmodulated reactionzone, the retro-aldol and hydrogenation conversion conditions need to bein balance.

A desire thus exists to provide methods for controllingretro-aldol/hydrogenation processes using an unmodulated reaction zone.Moreover, it is desired that such methods use input parameters that canbe reasonably obtained from the process, especially input parametersthat can be ascertained relatively quickly to provide real-time dataregarding the operation of the process.

BRIEF SUMMARY

By this invention processes are provided for the conversion ofcarbohydrate to ethylene glycol by retro-aldol catalysis and sequentialhydrogenation using control methods having at least one of acetol(hydroxyacetone) and at least one tracer as inputs. A tracer precursoris one or more ketones of 3 to 6, preferably 4 to 6, carbons and thetracer is one or more of unreacted tracer precursor and hydrogenationproducts of the ketone such as alcohols in the raw product resultingfrom the supply of the ketone to the reaction zone. Acetol concentrationin raw product reflects both information about the relative amount ofaldose isomerization as it is a three-carbon compound derived from theretro-aldol catalysis of fructose and the hydrogenation. A carbonyl of aketone does not undergo retro-aldol conversion, and thus the tracerreflects on hydrogenation strength. Since the conversion of carbohydratedoes not result in the coproduction of hydrocarbons only having internalcarbonyls or internal hydroxyls, the input based upon one or moretracers is not confounded as a coproduct. The control systems useful forthe retro-aldol/hydrogenation conversion of carbohydrate to ethyleneglycol will employ a number of other inputs such as one or more ofpressure, temperature, residence time, pH, raw product composition, feedcompositions and rates, and the like. Acetol and/or tracer provideinformation not otherwise readily available about the condition of theprocess, and thus their use as inputs to a control system can provide amore robust and useful control of the process. Increases in acetolconcentration in the raw product have been found by this invention topresage an observable decrease in selectivity to ethylene glycol. Hence,process changes can be implemented timely to maintain conversion andselectivity to ethylene glycol. Similarly, the tracer specificallytargets hydrogenation activity and facilitates unconfounding whether achange in a by-product or product production is due to issues with theretro-aldol catalytic activity or hydrogenation catalytic activity.

Any suitable process control system can be used, and more expansivecontrol systems for the process which systems can be design spacesystems (DSC) or model predictive control systems (MPC), both of whichare well known in the art, are often preferred. In a DSC, boundaryconditions, or windows, are predetermined and operation within thewindows is considered to be under control. In an MPC, dynamic processmodels, which are often empirically generated, take into account currentcontrol status as well as its effect on the process in the future.Control actions in an MPC can be taken based upon the predictive modelsin anticipation of future events. However, the disclosed processes whichuse either or both of acetol and tracer in the raw product, enhance theability to control the process regardless of whether the control ismanual or based on sophisticated control systems.

One broad aspect pertains to a continuous processes having a controlsystem to control one or more operating parameters based on one or moreinputs for the catalytic conversion of a carbohydrate feed containing atleast aldose-yielding or ketose-yielding carbohydrate to lower glycol ofat least one of ethylene glycol and propylene glycol in an unmodulatedreaction zone by sequential retro-aldol catalytic conversion underretro-aldol conditions, including the presence of a retro-aldol catalystproviding retro-aldol catalytic activity in liquid medium in theunmodulated reaction zone, to intermediates and catalytic hydrogenationof intermediates under hydrogenation conditions, including the presenceof hydrogen and hydrogenation catalyst providing hydrogenation catalyticactivity, to lower glycol, in the unmodulated reaction zone, andwithdrawing continuously or intermittently from said unmodulatedreaction zone, a raw product, said process comprising controlling atleast one operating parameter of the process using at least theconcentration of acetol in the raw product is an input to the controlsystem for the process. Preferably the carbohydrate comprises aldose andthe lower glycol comprises ethylene glycol.

Acetol is derived from fructose, and thus its concentration is dependentupon the fructose generated, and thus changes in the concentration offructose need to be taken into account. In preferred processes formaking ethylene glycol, in response to an increase in acetolconcentration without evidence of a reduction in retro-aldol catalyticactivity, at least one of (i) the hydrogenation catalytic activity isincreased and (ii) at least one of the rate of supply of thecarbohydrate feed and the concentration of the carbohydrate in the feed,is decreased. Where evidence of a reduction in retro-aldol catalyticactivity exists, for instance, with an increase in mannitol or glycerol,an increase in acetol, if greater than expected from the reduction inretro-aldol catalytic activity, would indicate that at least one of therate of supply of the carbohydrate feed and the concentration of thecarbohydrate in the feed, is decreased until the retro-aldol catalyticactivity is reestablished.

Another broad aspect pertains to continuous processes having a controlsystem to control one or more operating parameters based on input forthe catalytic conversion of a carbohydrate feed containing at leastaldose-yielding or ketose-yielding carbohydrate to lower glycol of atleast one of ethylene glycol and propylene glycol in an unmodulatedreaction zone by sequential retro-aldol catalytic conversion underretro-aldol conditions, including the presence of a retro-aldol catalystproviding retro-aldol catalytic activity in a liquid medium in theunmodulated reaction zone, to intermediates and catalytic hydrogenationof intermediates under hydrogenation conditions, including the presenceof hydrogen and hydrogenation catalyst providing hydrogenation catalyticactivity, to lower glycol, in the unmodulated reaction zone, supplying aketone of 3 to 6, preferably 4 to 6, carbons to the reaction zone fromwhich a tracer is produced under conditions in the reaction zone andwithdrawing continuously or intermittently from said unmodulatedreaction zone, a raw product, said process comprising controlling atleast one operating parameter of the process using at least theconcentration of at least one component of the tracer in the raw productis an input value to the control system for the process.

Where the tracer indicates a change in the hydrogenation of the ketone,preferably the at least one of (i) the absolute amounts of catalyticallyactive species and relative amounts of each of the retro-aldol catalyticactivity and hydrogenation catalytic activity, and (ii) at least one ofthe rate of feed, and carbohydrate concentration, to the reaction zoneare adjusted. Where more ketone is hydrogenated, often at least the rateof feed to the reaction zone is increased or the hydrogenation catalyticactivity is decreased. Where less ketone is hydrogenated, preferablyeither or both of (i) the hydrogenation catalyst activity in thereaction zone is increased and (ii) at least one of the rate of feed andthe concentration of carbohydrate to the reaction zone is decreased.

In many instances, the retro-aldol catalyst is homogeneous and thehydrogenation catalyst is heterogeneous. The desired process objectiveis often the selectivity of conversion to ethylene glycol, and in someinstances, the selectivity to the total of ethylene glycol and propyleneglycol (“total lower glycol”) is greater than about 75 mass percentbased upon the mass of the feed. In some instances, the concentrationsof acetol or at least one component of the tracer can be compared withconcentrations of at least one of itol, 1,2-butanediol, pH and, in thecase of acetol, tracer if used, and in the case of tracer being used,acetol, in the raw product for purposes of process control. The reactionprocess can be a cascade process or a single pot process. When makingethylene glycol, acetol concentrations are often compared toconcentrations of at least one of sorbitol, 1.2-butanediol and glycerol.When making ethylene glycol, tracer concentrations are often comparedwith concentrations of at least one of sorbitol and glycerol.

The use of a tracer precursor can be continuous or intermittent. Forinstance, the tracer precursor can be used intermittently to assure thatthe process is performing as desired or to assist in troubleshooting aproblem in the operation of the process and to bring the process backinto alignment with desired operation. The disclosed processes can alsobe used, e.g., in laboratory or pilot scale operations, to evaluatehydrogenation catalysts and hydrogenation catalytic activity forresearch, development or qualification purposes, or can be used toevaluate ex-situ samples of catalyst and hydrogenation catalyticactivity being used or to be used in a larger, e.g., commercial-scaleprocess. The ex-situ evaluations can be used as a parameter for use inthe control system for the process.

While multiple embodiments are disclosed, still other embodiments of thedisclosure will become apparent to those skilled in the art from thefollowing detailed description, which shows and describes illustrativeembodiments of the invention. As will be realized, the disclosure iscapable of modifications in various obvious aspects, all withoutdeparting from the spirit and scope of the disclosure. Accordingly, thedrawings and detailed description are to be regarded as illustrative innature and not restrictive.

DETAILED DESCRIPTION

All patents, published patent applications and articles referencedherein are hereby incorporated by reference in their entirety.

Definitions

As used herein, the following terms have the meanings set forth belowunless otherwise stated or clear from the context of their use.

Where ranges are used herein, the end points only of the ranges arestated so as to avoid having to set out at length and describe each andevery value included in the range. Any appropriate intermediate valueand range between the recited endpoints can be selected. By way ofexample, if a range of between 0.1 and 1.0 is recited, all intermediatevalues (e.g., 0.2, 0.3, 0.63, 0.815 and so forth) are included as areall intermediate ranges (e.g., 0.2-0.5, 0.54-0.913, and so forth).

The use of the terms “a” and “an” is intended to include one or more ofthe element described.

Admixing or admixed means the formation of a physical combination of twoor more elements which may have a uniform or non-uniform compositionthroughout and includes, but is not limited to, solid mixtures,solutions and suspensions.

Bio-sourced carbohydrate feedstock means a product that includescarbohydrates sourced, derived or synthesized from, in whole or insignificant part, to biological products or renewable agriculturalmaterials (including, but not limited to, plant, animal and marinematerials) or forestry materials.

By-products are incidental or secondary products made in the manufactureof the sought product and include the incidental or secondary productsand intermediates to these products and include reaction products fromthe sought product. By-products do not include intermediates to thesought product. By way of example, in the catalytic conversion ofglucose to ethylene glycol, any unreacted glycol aldehyde would not be aby-product but hydroxyacetone would be a byproduct, even though eithermight be able to be further reacted under the conditions of thereaction. Other by-products include, but are not limited to, mannitol,sorbitol, glycerol, 1,2-butanediol, erythritol, threitol, organic acids,and gases.

Catalyst means a heterogeneous or homogeneous catalyst. For purposesherein, catalysts that behave as if they are dissolved in the media,e.g., a colloidal suspension, are considered to be homogeneous catalystsregardless of whether or not they are dissolved. A catalyst can containone or more catalytic metals, and for heterogeneous catalysts, includesupports, binders and other adjuvants. Catalytic metals are metals thatare in their elemental state or are ionic or covalently bonded. The termcatalytic metals refers to metals that are not necessarily in acatalytically active state, but when not in a catalytically activestate, have the potential to become catalytically active. Catalyticmetals can provide catalytic activity or modify catalytic activity suchas promotors, selectivity modifiers, and the like.

Catalytic activity or performance refers to the extrinsic activity of acatalyst in the reaction zone. Thus, the factors that affect catalystactivity include the condition of the catalyst per se, but also includeits deployment in the reaction zone. For example, if a portion of thecatalyst is physically occluded in the reaction zone, it is relativelyunavailable for effecting the sought catalytic conversion even though itmay be active per se. Mixing or other means of redistribution to makethe catalyst surface accessible would thus improve the extrinsiccatalytic activity.

A change in catalytic activity can result from a change in the catalystper se such as a chemical change, physical degradation, redistributionof components on the catalyst, loss of catalytically-active species fromthe catalyst, or poisoning or other effect from a component that becomedeposited or reacted during the course of the reaction. A change incatalytic activity can also be caused by the environment around thecatalyst where the catalyst itself may be relatively unchanged, e.g.,through steric effects or reactions or complexing with the components tobe catalytically converted. Therefore, an increase or decrease incatalytic activity can, but does not necessarily, result from anincrease or decrease in the mass of catalyst per unit volume.

Commencing contact means that a fluid starts a contact with a component,e.g., a medium containing a homogeneous or heterogeneous catalyst, butdoes not require that all molecules of that fluid contact the catalyst.

Conversion efficiency is the mass percent of a raw material that isconverted in the process to chemical product.

Hydraulic distribution means the distribution of an aqueous solution ina vessel including contact with any catalyst contained therein.

Intermediate means a compound that can be further reacted under theconditions in the reaction zone to the sought product. As definedherein, an intermediate to a by-product is itself deemed to be aby-product.

Intermittently means from time to time and may be at regular orirregular time intervals.

Input values mean input information from the process for the controlmethod. The inputs can be manipulative inputs, sometimes referred to asindependent variables, which means that the value being reported issubject to control such as temperature. The inputs can be processparameters, sometimes referred to as dependent variables, which meansthat the determined value is resulting from multiple manipulativevariables in the process. For instance, concentration of anintermediate, by-product or chemical product is the result of thecombined set of process conditions. An input value can be from one ortwo or more manipulative inputs and process parameter inputs and canrequire calculations. For example, conversion efficiency can bedetermined from raw material concentration in the feed and the feed rateto the reaction zone and from the concentration of the chemical productin the effluent from the reaction zone and the flow rate of theeffluent.

Itols are polyhydric alcohols with each carbon having a hydroxyl group,e.g., sugar alcohols.

Liquid medium means the liquid in the reactor. The liquid is a solventfor the carbohydrate, intermediates and products and for thehomogeneous, tungsten-containing retro-aldol catalyst. Typically andpreferably, the liquid contains at least some water and is thus termedan aqueous medium.

Operating parameters, or process parameters for the process arecontrollable parameters including, but not limited to temperature,pressure, feed rates and concentrations of reactants, residence time,adjuvants, pH, and hydrogenation catalytic activity and retro-aldolcatalytic activity.

Organics capable of being hydrogenated (“HOC's”) are oxygen-containinghydrocarbons capable of being hydrogenated under process conditions toone or more products. HOC's include, but are not limited to, sugars andother ketones and aldehydes and hydroxyl-containing hydrocarbons such asalcohols, diols and itols.

The pH of an aqueous solution is determined at ambient pressure andtemperature. In determining the pH of, for example the aqueous,hydrogenation medium or the product solution, the liquid is cooled andallowed to reside at ambient pressure and temperature for 2 hours beforedetermination of the pH. Where the solution for which the pH measurementis sought contains less than about 50 mass percent water, water is addedto the solution to provide greater than 50 mass percent water. Forpurposes of consistency, the dilution of solutions is to the same masspercent water.

pH control agents mean one or more of buffers and acids or bases.

The term raw material is used to indicate one or more reactant that areadded to the reaction zone in the process and is not intended to reflecton purity or need for refining. The raw material can be a product fromanother chemical or biochemical process. Since reactants includeintermediates, the term raw material thus facilitates understanding.

A reaction zone is the volume that contains the first and secondcatalyst and can be a single vessel or plural vessels, or reactors.

A reactor can be one or more vessels in series or in parallel and avessel can contain one or more zones. A reactor can be of any suitabledesign for continuous operation including, but not limited to, tanks andpipe or tubular reactors and can have, if desired, fluid mixingcapabilities. Types of reactors include, but are not limited to, laminarflow reactors, fixed bed reactors, slurry reactors, fluidized bedreactors, moving bed reactors, simulated moving bed reactors,trickle-bed reactors, bubble column and loop reactors.

Discussion

The processes for the conversion of carbohydrate that contains analdohexose-yielding carbohydrate or ketose-yielding carbohydrate to atleast one of ethylene glycol and propylene glycol (lower glycol) in areaction zone are effected by subjecting the sugar to catalyticretro-aldol conditions to produce intermediate that is hydrogenatedunder catalytic hydrogenation conditions. See, for instance, U.S.published patent applications 2017/0349513 and 2018/0086681 and U.S.Pat. Nos. 9,399,610 and 9,783,472, all hereby incorporated by referencein their entireties.

The raw material comprises carbohydrate which is most often at least oneof pentose and hexose or compounds that yield pentose or hexose.Examples of pentose and hexose include xylose, lyxose, ribose,arabinose, xylulose, ribulose, glucose, mannose, galactose, allose,altrose, idose, talose, and gulose fructose, psicose, sorbose, andtagatose. Most bio-sourced carbohydrate feedstocks yield glucose uponbeing hydrolyzed. Glucose precursors include, but are not limited to,maltose, trehalose, cellobiose, kojibiose, nigerose, nigerose,isomaltose, β,β-trehalose, α,β-trehalose, sophorose, laminaribiose,gentiobiose, and mannobiose. Carbohydrate polymers and oligomers such ashemicellulose, partially hydrolyzed forms of hemicellulose,disaccharides such as sucrose, lactulose, lactose, turanose, maltulose,palatinose, gentiobiulose, melibiose, and melibiulose, or combinationsthereof may be used.

The carbohydrate feed can be solid or, preferably, in a liquidsuspension or dissolved in a solvent such as water. Where thecarbohydrate feed is in a non-aqueous environment, it is preferred thatthe carbohydrate is at least partially hydrated. Non-aqueous solventsinclude alkanols, diols and polyols, ethers, or other suitable carboncompounds of 1 to 6 carbon atoms. Solvents include mixed solvents,especially mixed solvents containing water and one of the aforementionednon-aqueous solvents. Certain mixed solvents can have higherconcentrations of dissolved hydrogen under the conditions of thehydrogenation reaction and thus reduce the potential for hydrogenstarvation. Preferred non-aqueous solvents are those that can behydrogen donors such as isopropanol. Often these hydrogen donor solventshave the hydroxyl group converted to a carbonyl when donating a hydrogenatom, which carbonyl can be reduced under the conditions in the reactionzone. Most preferably, the carbohydrate feed is provided in an aqueoussolution. In any event, the volume of feed and the volume of raw productwithdrawn need to balance to provide for a continuous process.

Further considerations in providing the carbohydrate to the reactionzone are minimizing energy and capital costs. For instance, in steadystate operation, the solvent contained in the feed exits the reactionzone with the raw products and needs to be separated in order to recoverthe sought glycol products.

Preferably, the feed is introduced into the reaction zone in a mannersuch undue concentrations of HOC's that can result in hydrogenstarvation are avoided. With the use of a greater number of multiplelocations for the supply of carbohydrate per unit volume of the reactionzone, the more concentrated the carbohydrate in the feed can be. Ingeneral, the mass ratio of water to carbohydrate in the carbohydratefeed is preferably in the range of 4:1 to 1:4. Aqueous solutions of 600or more grams per liter of certain carbohydrates such as dextrose andsucrose are sometimes commercially available.

The carbohydrate contained in the carbohydrate feed is provided at arate of at least 50 or 100, and preferably, from about 150 to 500 gramsper liter of reactor volume per hour. Optionally, a separate reactionzone can be used that contains retro-aldol catalyst with an essentialabsence of hydrogenation catalyst.

In these processes, an liquid medium containing the carbohydrate iscontacted with retro-aldol catalyst under retro-aldol reactionconditions. The contact may commence prior to or upon introducing theliquid medium into a hydrogenation catalyst-containing portion of thereaction zone. The preferred temperatures for retro-aldol reactions aretypically from about 230° C. to 300° C., and more preferably from about240° C. to 280° C., although retro-aldol reactions can occur at lowertemperatures, e.g., as low as 90° C. or 150° C. The pressures (absolute)are typically in the range of about 15 to 200 bar (1500 to 20,000 kPa),say, from about 25 to 150 bar (2500 and 15000 kPa).

Retro-aldol reaction conditions include the presence of retro-aldolcatalyst. A retro-aldol catalyst is a catalyst that catalyzes theretro-aldol reaction. Examples of compounds that can provide retro-aldolcatalyst include, but are not limited to, heterogeneous and homogeneouscatalysts, including catalyst supported on a carrier, comprisingtungsten and its oxides, sulfates, phosphides, nitrides, carbides,halides, acids and the like. Tungsten carbide, soluble phosphotungstens,tungsten oxides supported on zirconia, alumina and alumina-silica arealso included. Preferred catalysts are provided by soluble tungstencompounds and mixtures of tungsten compounds. Soluble tungstatesinclude, but are not limited to, ammonium and alkali metal, e.g., sodiumand potassium, paratungstate, partially neutralized tungstic acid,ammonium and alkali metal metatungstate and ammonium and alkali metaltungstate. Often the presence of ammonium cation results in thegeneration of amine by-products that are undesirable in the lower glycolproduct. Without wishing to be limited to theory, the species thatexhibit the catalytic activity may or may not be the same as the solubletungsten compounds introduced as a catalyst. Rather, a catalyticallyactive species may be formed as a result of exposure to the retro-aldolreaction conditions. Tungsten-containing complexes are typically pHdependent. For instance, a solution containing sodium tungstate at a pHgreater than 7 will generate sodium metatungstate when the pH islowered. The form of the complexed tungstate anions is generally pHdependent. The rate that complexed anions formed from the condensationof tungstate anions are formed is influenced by the concentration oftungsten-containing anions. A preferred retro-aldol catalyst comprisesammonium or alkali metal tungstate that becomes partially neutralizedwith acid, preferably an organic acid of 1 to 6 carbons such as, butwithout limitation, formic acid, acetic acid, glycolic acid, and lacticacid. The partial neutralization is often from about 25 to 75%, i.e., onaverage from 25 to 75% of the cations of the tungstate become acidsites. The partial neutralization may occur prior to introducing thetungsten-containing compound into the reactor or with acid contained inthe reactor.

The concentration of retro-aldol catalyst used may vary widely and willdepend upon the activity of the catalyst and the other conditions of theretro-aldol reaction such as acidity, temperature and concentrations ofcarbohydrate. Typically, the retro-aldol catalyst is provided in anamount to provide from about 0.01 or 0.05 to 100, say, from about 0.02or 0.1 to 50, grams of tungsten calculated as the elemental metal perliter of aqueous, hydrogenation medium. The retro-aldol catalyst can beadded as a mixture with all or a portion of the carbohydrate feed or asa separate feed to the aqueous, hydrogenation medium or with recyclingliquid medium or any combination thereof. In some instances, ahomogeneous, tungsten-containing retro-aldol catalyst can deposit atungsten-containing compound or complex on the hydrogenation catalystand adversely affect the activity of the hydrogenation catalyst. Acontinuous or intermittent cycling of the amount of tungsten-containingcatalyst can result in removal of at least a portion of the depositedtungsten compound or complex. The disclosed methods thus contemplatethat the control of the absolute amount of catalytically active speciesand relative amounts of each of the first catalyst and second catalystincludes operations where the process objective is a rejuvenation of acatalyst. The disclosed methods also contemplate that the control of theabsolute amount of catalytically active species and relative amounts ofeach of the first catalyst and second catalyst includes operations wherethe process objective is a reduction of the catalytic activity of one ofthe first or second catalysts. The reduction in the catalytic activitycan be achieved by any suitable means, including, but not limited to,one or more of reducing the concentration of the catalyst in the liquidmedium, selective poisoning of catalytically active species of thecatalyst, and providing additives or modifiers that reduce catalyticactivity without necessarily reducing catalytically active species.

Frequently the carbohydrate feed is subjected to retro-aldol conditionsprior to being introduced into the aqueous, hydrogenation medium in thereaction zone containing hydrogenation catalyst. Preferably theintroduction into the aqueous, hydrogenation medium occurs in less thanone minute, and most often less than10 seconds, from the commencement ofsubjecting the carbohydrate feed to the retro-aldol conditions. Some, orall of the retro-aldol reaction can occur in the reaction zonecontaining the hydrogenation catalyst. In any event, the most preferredprocesses where isomerization of glucose to fructose is undesirable, arethose having a short duration of time between the retro-aldol conversionand hydrogenation.

The hydrogenation, that is, the addition of hydrogen atoms to an organiccompound without cleaving carbon-to-carbon bonds, can be conducted at atemperature in the range of about 100° C. or 120° C. to 300° C. or more.Typically, the aqueous, hydrogenation medium is maintained at atemperature of at least about 230° C. until substantially allcarbohydrate is reacted to have the carbohydrate carbon-carbon bondsbroken by the retro-aldol reaction, thereby enhancing selectivity toethylene and propylene glycol. Thereafter, if desired, the temperatureof the aqueous, hydrogenation medium can be reduced. However, thehydrogenation proceeds rapidly at these higher temperatures. Thus, thetemperatures for hydrogenation reactions are frequently from about 230°C. to 300° C., say, from 240° C. to 280° C. The pressures are typicallyin the range of about 15 to 200 bar, say, from about 25 to 150 bar. Thehydrogenation reactions require the presence of hydrogen as well ashydrogenation catalyst. Hydrogen has low solubility in aqueoussolutions. The concentration of hydrogen in the aqueous, hydrogenationmedium is increased with increased partial pressure of hydrogen in thereaction zone. The pH of the aqueous, hydrogenation medium is often atleast about 3, say, from about 3 or 3.5 to 8, and in some instances fromabout 3.2 or 4 to 7.5.

The hydrogenation is conducted in the presence of a hydrogenationcatalyst. Frequently the hydrogenation catalyst is a heterogeneouscatalyst. It can be deployed in any suitable manner, including, but notlimited to, fixed bed, fluidized bed, trickle bed, moving bed, slurrybed, and structured bed. Nickel, ruthenium, palladium and platinum areamong the more widely used reducing metal catalysts. However, manyreducing catalysts will work in this application. The reducing catalystcan be chosen from a wide variety of supported transition metalcatalysts. Nickel, Pt, Pd and ruthenium as the primary reducing metalcomponents are well known for their ability to reduce carbonyls. Oneparticularly favored catalyst for the reducing catalyst in this processis a supported, Ni-Re catalyst. A similar version of Ni/Re or Ni/Ir canbe used with good selectivity for the conversion of the formedglycolaldehyde to ethylene glycol. Nickel-rhenium is a preferredreducing metal catalyst and may be supported on alumina, alumina-silica,silica or other supports. Supported Ni-Re catalysts with B as a promoterare useful. Generally, for slurry reactors, a supported hydrogenationcatalyst is provided in an amount of less than 10, and sometimes lessthan about 5, say, about 0.1 or 0.5 to 3, grams per liter of nickel(calculated as elemental nickel) per liter of liquid medium in thereactor. As stated above, not all the nickel in the catalyst is in thezero-valence state, nor is all the nickel in the zero-valence statereadily accessible by glycol aldehyde or hydrogen. Hence, for aparticular hydrogenation catalyst, the optimal mass of nickel per literof liquid medium will vary. For instance, Raney nickel catalysts wouldprovide a much greater concentration of nickel per liter of liquidmedium. Frequently in a slurry reactor, the hydrogenation catalyst isprovided in an amount of at least about 5 or 10, and more often, fromabout 10 to 70 or 100, grams per liter of aqueous, hydrogenation mediumand in a packed bed reactor the hydrogenation catalyst comprises about20 to 80 volume percent of the reactor. In some instances, the weighthourly space velocity is from about 0.01 or 0.05 to 1 hr⁻¹ based upontotal carbohydrate in the feed. Preferably the residence time issufficient that glycol aldehyde and glucose are less than 0.1 masspercent of the reaction product, and most preferably are less than 0.001mass percent of the reaction product.

In the disclosed processes, the combination of reaction conditions(e.g., temperature, hydrogen partial pressure, concentration ofcatalysts, hydraulic distribution, and residence time) are sufficient toconvert at least about 95, often at least about 98, mass percent andsometimes essentially all of the carbohydrate that yield aldose orketose. It is well within the skill of the artisan having the benefit ofthe disclosure herein to determine the set or sets of conditions thatwill provide the sought conversion of the carbohydrate.

Optimizing the retro-aldol process to make ethylene glycol involvesoptimizing the retro-aldol conversion, which is primarily kineticlimited, and the hydrogenation reaction which is primarily mass transferlimited. Mass transfer limitations include the supply of hydrogen to thehydrogenation catalytic sites, and hydrogen starvation can occur wherelocalized regions of high hydrogenation catalytic active exist. Thehydrogen starvation can be caused by, by way of example and not inlimitation, maldistribution of the hydrogenation catalyst within thereaction zone and localized regions of higher feed concentration in thereaction zone. Hydrogen starvation thus can result in the formation oforganic acids, and organic acids can be a by-product in the withdrawnmedium. For purposes of process control, pH determinations can often beused as a proxy for organic acid concentration. In some instances,reducing the rate of feed can attenuate the generation of acids;however, manipulation of one or both of the absolute amount and relativeamounts of retro-aldol catalyst and hydrogenation catalyst may also berequired.

The acetol or tracer is often used in connection with other parameterobservations. Especially with acetol, which presages observablereductions in conversion and selectivity to ethylene glycol, a changecan be used to trigger reviewing changes in other parameters toascertain process changes to be made to prevent a significant disruptionof the process, and preferably, avoid material losses of conversion andselectivity to ethylene glycol. In one embodiment, an increase in acetoltriggers the addition of a tracer precursor to evaluate catalytichydrogenation activity or triggers a removal of a portion of thehydrogenation catalyst for an ex-situ evaluation.

Frequently, an additional process parameter input for process control isthe concentration in the withdrawn medium of at least one of itol and1,2-butanediol. The itols contained in the withdrawn medium result fromreactions with the carbohydrate feed. Glucose, for instance, can behydrogenated to sorbitol. In the retro-aldol step, glucose can provideglycol aldehyde and erythrose and, if isomerized, threose. These fourcarbon sugars, when hydrogenated, produce erythritol and threitol.Glucose can also undergo isomerization to fructose, and fructose, whenhydrogenated, go to mannitol and sorbitol. Also, fructose underretro-aldol conditions, goes to three carbon compounds and thus glycerolcan be produced. Because of the genesis of the itols, insights into theprocess can be obtained from the type and the rate of production of theitols.

As a general matter, an increase in itol concentration, all other thingsremaining substantially constant, is indicative that the retro-aldolcatalytic activity has suffered, and one example of a manipulativeinputs would be an adjustment to at least one of (I) the absolute amountand relative amounts of each of the retro-aldol catalytic activity andhydrogenation catalytic by increasing the retro-aldol catalytic activityor decreasing the hydrogenation catalytic activity, and (II) reducingthe rate of feed of the raw material to the reaction zone.

If 1,2-butanediol concentration is used as a process parameter input,the 1,2-butanediol can result from the reaction between twoglycolaldehyde molecules or from the dehydration of a tetrose. In theformer, the general rule is that an increase in the 1,2-butanediolconcentration is reflecting a loss of hydrogenation catalyst activity inthe reaction zone, all other things remaining substantially the same. Inthis case, an example of an adjustment of manipulative inputs would beto at least one of (I) the absolute amount and relative amounts of eachof the retro-aldol catalyst and hydrogenation catalyst by increasing thecatalyst activity of the hydrogenation catalyst or decreasing thecatalyst activity of the retro-aldol catalyst, and (II) reducing therate of feed of the raw material to the reaction zone. In the latter,the retro-aldol conversion activity is likely inadequate, and (I)increasing activity of the retro-aldol catalyst, and (II) at least oneof reducing the rate of feed of the raw material and its concentrationto the reaction zone, would be responsive actions. Thus, having anotherparameter to directionally indicate whether the change in concentrationof 1,2-butanediol can be helpful. For example, if an increase in1,2-butandiol is accompanied by an increase in glycerol, which is madefrom fructose, which is from the isomerization of glucose, would beindicative of a reduction in retro-aldol activity since theisomerization reaction is out pacing the retro-aldol conversions, allelse remaining the same.

Acetol is usually present in the withdrawn medium in a very lowconcentration. It has been found, however, that an increase of acetol isa sensitive indicator of a decrease in activity of the hydrogenationcatalyst, especially where the concentration of fructose has notsubstantially changed. An increase in acetol concentration, under thesecircumstances can be addressed by increasing the catalytic activity ofthe hydrogenation catalyst and/or reducing the rate of raw material feedor its concentration to the reaction zone. In some instances, the acetolconcentration in the withdrawn medium is less than 0.15 mass percent,preferably less than 0.10 mass percent.

A tracer can be used similarly to acetol. Ketones such as methyl ethylketone are useful to provide tracers for the retro-aldol/hydrogenationprocess as the internal carbonyl is more resistant to hydrogenation thanthe carbonyl of an aldehyde. The extent of hydrogenation of the ketoneis thus an indicator of the hydrogenation activity in the reaction zone.The concentration of the ketone can vary widely and will depend upon,for instance, the ability to analytically detect the concentration of atracer in the withdrawn medium. Often the concentration of the tracer isin the range of between about 1 part per million to 1 percent, by massbased upon mass of the medium.

The control system and control system hardware used is not critical tothe broad processes of this invention, and any suitable control system,including manual, can be used. Design space and model predictive controlare well known and are multivariate and are preferred. The former isbased upon models and manipulative inputs values are maintained towindows of acceptable operation. Where manipulative inputs areinterrelated, the design space control systems can be designed withpredictive models such that adjustments in one manipulative inputcoincide with adjustments in one or more other manipulative inputs. Thelater considers not only the instantaneous state of the process but alsothe future state of the process. The models can be developed on, forinstance, a linear or quadratic models. These models can be derived fromempirical data and the performance of the process with respect toprocess objectives. With respect to model predictive control, data fromthe process can be used to refine the future predictive aspect of themodels. The control systems can be open loop or closed loop, and whereclosed loop, the loop can be the entire plant or a portion thereof.

Although the disclosure has been described with references to variousembodiments, persons skilled in the art will recognized that changes maybe made in form and detail without departing from the spirit and scopeof this disclosure.

What is claimed is:
 1. A continuous process having a control system tocontrol one or more operating parameters based on one or more inputs forthe catalytic conversion of a carbohydrate feed containing at leastaldose-yielding or ketose-yielding carbohydrate to lower glycol of atleast one of ethylene glycol and propylene glycol in an unmodulatedreaction zone by sequential retro-aldol catalytic conversion underretro-aldol conditions, including the presence of a retro-aldol catalystproviding retro-aldol catalytic activity in a liquid medium in theunmodulated reaction zone, to intermediates and catalytic hydrogenationof intermediates under hydrogenation conditions, including the presenceof hydrogen and hydrogenation catalyst providing hydrogenation catalyticactivity, to lower glycol, in the unmodulated reaction zone, andwithdrawing continuously or intermittently from said unmodulatedreaction zone, a raw product, said process comprising controlling atleast one operating parameter of the process using at least theconcentration of acetol in the raw product is an input to the controlsystem for the process.
 2. The process of claim 1 wherein thecarbohydrate comprises aldose and the lower glycol comprises ethyleneglycol.
 3. The process of claim 2 wherein in response to an increase inacetol concentration, at least one of (i) the hydrogenation catalyticactivity is increased and (ii) at least one of the rate of supply of thecarbohydrate feed and the concentration of carbohydrate in the feed isdecreased.
 4. The process of claim 2 wherein the retro-aldol catalyst ishomogeneous and the hydrogenation catalyst is heterogeneous.
 5. Theprocess of claim 2 wherein the concentration of acetol is compared withconcentrations of at least one of itol, 1,2-butanediol, and pH in theraw product for purposes of process control.
 6. The process of claim 5wherein in response to an increase in acetol concentration and anincrease in the concentration of at least one of sorbitol,1,2-butanediol, and glycerol in the raw product, the retro-aldolcatalytic activity is increased.
 7. The process of claim 2 wherein thehydroxyacetone concentration is maintained less than about 0.15 masspercent of the raw product.
 8. The process of claim 2 wherein inresponse to an increase in acetol accompanied by an increase in at leastone of mannitol and glycerol, at least one of the rate of supply of thecarbohydrate feed and the concentration of the carbohydrate in the feed,is decreased until retro-aldol catalytic activity is increased.
 9. Theprocess of claim 1 wherein the reaction zone is a cascade reaction zone.10. A continuous process having a control system to control one or moreoperating parameters based on input for the catalytic conversion of acarbohydrate feed containing at least aldose-yielding or ketose-yieldingcarbohydrate to lower glycol of at least one of ethylene glycol andpropylene glycol in an unmodulated reaction zone by sequentialretro-aldol catalytic conversion under retro-aldol conditions, includingthe presence of a retro-aldol catalyst providing retro-aldol catalyticactivity in a liquid medium in the unmodulated reaction zone, tointermediates and catalytic hydrogenation of intermediates underhydrogenation conditions, including the presence of hydrogen andhydrogenation catalyst providing hydrogenation catalytic activity, tolower glycol, in the unmodulated reaction zone, supplying a tracerprecursor comprising a ketone of 3 to 6 carbons to the reaction zonefrom which at least one tracer is produced under conditions in thereaction zone and withdrawing continuously or intermittently from saidunmodulated reaction zone, a raw product, said process comprisingcontrolling at least one operating parameter of the process using atleast the concentration of at least one component of the tracer in theraw product is an input to the control system for the process.
 11. Theprocess of claim 10 wherein where the tracer in the raw productindicates a change in the portion of the tracer precursor hydrogenated,then at least one of (i) the absolute amounts of catalytically activespecies and relative amounts of each of the retro-aldol catalyticactivity and hydrogenation catalytic activity, and (ii) at least one ofthe rate of feed and concentration of carbohydrate in the feed to thereaction zone are adjusted.
 12. The process of claim 11 where theconcentration of a tracer in the raw product indicates that a greaterportion of the tracer precursor is hydrogenated, either or both the rateof feed to the reaction zone is increased or the hydrogenation catalystactivity in the reaction zone is decreased.
 13. The process of claim 11where the concentration of a tracer in the raw product indicates that alesser portion of the tracer precursor is hydrogenated, either or bothof (i) the hydrogenation catalyst activity in the reaction zone isincreased and (ii) at least one of the rate of feed and theconcentration of carbohydrate in the feed to the reaction zone isdecreased.
 14. The process of claim 10 wherein the retro-aldol catalystis homogeneous and the hydrogenation catalyst is heterogeneous.
 15. Theprocess of claim 10 wherein the carbohydrate comprises aldose and thelower glycol comprises ethylene glycol, concentrations of at least onecomponent of the tracer is compared with concentrations of at least oneof itol, 1,2-butanediol, acetol and pH in the raw product for purposesof process control.
 16. The process of claim 15 where the tracer in theraw product indicates a substantially constant in the portion of thetracer precursor being hydrogenated and an increase in the concentrationof at least one of sorbitol and glycerol in the raw product, theretro-aldol catalytic activity is increased.
 17. The process of claim 15where the tracer in the raw product indicates a decrease in the portionof the tracer precursor being hydrogenated and no increase in theconcentration of at least one of sorbitol, 1,2-butanediol, and glycerolin the raw product, one or both of (i) the hydrogenation catalyticactivity is increased and (ii) at least one of the feed rate and theconcentration of the carbohydrate in the feed is decreased.
 18. Theprocess of claim 10 wherein the process uses hydrogenation catalystwithdrawn from or intended to be used in a larger reaction zone forevaluating hydrogenation catalytic activity.
 19. The process of claim 10wherein the tracer precursor is added to trouble shoot the process. 20.The process of claim 10 wherein the tracer precursor comprisesmethylethylketone and the tracers comprise methylethylketone andiso-butanol.